As lighting products become more and more intelligent, various auxiliary circuits, such as sensors, radio frequency (RF) communication modules, or other accessory circuits may be added to the product. These auxiliary circuits require auxiliary bias supplies from driver circuits. As power consumption of the auxiliary circuits becomes considerable, the bias supplies should be generated with adequate efficiency and should remain stable even if the main output source or load of the lighting product is off.
An additional, standalone power converter that is independent from the main power converter used to drive the main output load can be used to generate the auxiliary bias supplies. However, such an additional converter increases the cost and size of the lighting product. Alternatively, the main converter used to drive the main output source can include an additional stage of power conversion in order to drive the auxiliary circuits. However, such an approach may provide relatively low power efficiency, especially if the voltage across the main output load is significantly higher than the voltage across the auxiliary load.
A third approach for generating the auxiliary bias supplies is to use voltage generated across secondary windings of a magnetic element, such as a transformer, of the main power converter. For some applications, in situations when the main output load is in a reduced or low power consumption mode (e.g., when the main light emitting diodes (LEDs) of the lighting product are in a dimmed or off state), it may still be desirable for the auxiliary circuits to be functioning in a normal operation mode, in which case a sufficient amount of energy needs to be supplied to the secondary windings to maintain the auxiliary bias voltage at a sufficiently high level. When the main output load is in the reduced or lower power consumption mode, it may consume no or a relatively small amount of current such that the bias voltage used to power the main output load stays relatively high. Power converters that monitor the output voltage of the main output load through feedback in order to control the supply of power may detect that the main output voltage is staying at a relatively high level and, in turn, determine to decrease the amount of power supplied from the magnetic element. However, this decrease in the amount of supplied power from the magnetic element may cause the auxiliary bias voltage to drop, causing the auxiliary circuits to undesirably stop operating. As such, ways to keep the auxiliary circuits operating while the main output load is in a reduced power consumption mode and while still utilizing the secondary windings of the magnetic element of the main converter may be desirable.